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From Erik Bengtson <e...@jpox.org>
Subject Re: [DISCUSS} Server TimeZone
Date Fri, 09 Feb 2007 08:48:32 GMT
Craig, I understand that server means the backend database server. what it we
have multiple backend db servers?

Use case with multiple dbs:

SELECT FROM db1.classA WHERE classA.time > datetime() && classB.time >
datetime() VARIABLES db2.classB

The first datetime() is evaluated by db1, while the second by db2.

Quoting Craig L Russell <Craig.Russell@Sun.COM>:

> Here is a proposal to add the ability of a user to get the time at
> the server in a portable way.
>
> This should allow an application to avoid time skew by using the time
> as seen by a single source, the server to which the
> PersistenceManagerFactory is connected.
>
> <proposed>
> 11.1
> ...
> ServerTimeZoneID: the time zone ID of the server to which this
> PersistenceManagerFactory is connected, for use with the
> PersistenceManager method getServerDate
> If ServerTimeZoneID is specified, the value must correspond to a
> valid time zone ID as returned by TimeZone.getAvailableIDs(). The
> implementation uses the ServerTimeZoneID to implement the
> getServerDate method. If ServerTimeZoneID is not specified, the
> implementation might use proprietary methods to determine the time
> zone in which the server is located. If ServerTimeZoneID is not
> specified, and the implementation cannot or does not use proprietary
> methods to determine the server time zone, then the default time zone
> ID of the Java VM is used.
>
> 12.17 Server Date
> java.util.Date getServerDate();
>
> Time skew is a phenomenon in which machines connected together in
> client/server configurations might have clocks that are not perfectly
> synchronized, and the time as seen by different clients might differ.
> In order for the application to avoid time skew, this method can be
> used to acquire a Date instance corresponding to the UTC Date as seen
> by the server. Clients using this method can order their operations
> according to a single time source.
> Implementations use the setting of the server time zone to prepare a
> Date instance that represents UTC time on the server.
> </proposed>
>
> Craig Russell
> Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
> 408 276-5638 mailto:Craig.Russell@sun.com
> P.S. A good JDO? O, Gasp!
>
>




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